For example, a drive device of an electric car adopts a configuration in which AC from a power collector, such as a pantograph sliding on wiring connected to an AC power supply, is converted to DC by a converter via a transformer, and DC is further converted to three-phase AC power via an inverter so as to drive a three-phase induction motor.
In the power conversion device in the related art of this type, a DC voltage at an output end of the converter is superimposed with a component that pulsates at twice the frequency of an AC power-supply voltage and this component becomes a factor of a beat in an output current of the three-phase induction motor. In order to suppress this beat phenomenon, there has been proposed a technique aimed at cancelling out a frequency twice the frequency of an AC power-supply voltage in the DC voltage by detecting a harmonic component twice the frequency of the AC power-supply voltage and adjusting a slip frequency of the induction motor on the basis of the detection result (see PTL 1 and PTL 2). By increasing a capacity of a smoothing capacitor provided to a DC stage, this pulsation frequency component can be reduced to some extent but cannot be removed completely. Also, such an increase of the capacity raises a problem that a size of the device becomes larger.